Most sampling devices which are designed to withdraw sample aliquots from successive sample specimens suffer from problems associated with the contamination of one sample specimen by material from a previous specimen.
This contamination arises as a result of sample material being deposited into a specimen by the sampling device itself, and of material remaining in the internal passageways of the sampling and analysis systems. To minimize this sample to sample contamination or "carryover" a number of sampling mechanisms have in the past been developed which provide for sampling of a wash solution between successive samples.
Furthermore, most analysis apparatus are essentially comparators and require the introduction of liquid calibration standards to ensure accuracy and to check their performance.
It is desirable that these standard solutions are introduced through the same path as any subsequent sample to be measured so that any pecularities of the system are common to both standard and samples. The method of measurement will then remove any such pecularities by relating the sample measurement to the standards measurement.
Previous sampling systems have used devices employing rotating or sliding valves at the input to the analysis apparatus to interchange the transmission of standard solutions and samples, or a probe arrangement that moves in two planes alternating between a receptacle containing the standard solution and/or a receptacle containing wash solution and the sample receptacle.
Valves and comparable mechanical devices are complicated, require precise machining and need a great deal of power to operate them. In addition, with the use of moving parts, failure of the seals is frequent, resulting in contamination of the standard with samples and vice versa. Furthermore, in the rotating valve system, the sample, wash and standard solutions do not follow the same path into the analysis apparatus.
Known probe arrangements have a relatively complicated mechanism to drive the probe between the sample and the wash solution receptacles and to move the probe into and out of these receptacles. In addition, contamination between the standard solution and the samples can occur since the probe is required to dip into a bulk of liquid. Thus, transference and hence contamination takes place between receptacles via the outside of the probe.
It is an object of the present invention to provide a sampling device which has a probe movable by means of a simple mechanism between a sample take-up position and a wash/standard solution supply.
It is a further object to provide a device having means to supply a flowing wash solution and/or a standard solution to the tip of a probe for up-take thereby.